Conditional spectrum‐based ground motion selection. Part I: Hazard consistency for risk‐based assessments

The conditional spectrum (CS, with mean and variability) is a target response spectrum that links nonlinear dynamic analysis back to probabilistic seismic hazard analysis for ground motion selection. The CS is computed on the basis of a specified conditioning period, whereas structures under consideration may be sensitive to response spectral amplitudes at multiple periods of excitation. Questions remain regarding the appropriate choice of conditioning period when utilizing the CS as the target spectrum. This paper focuses on risk‐based assessments, which estimate the annual rate of exceeding a specified structural response amplitude. Seismic hazard analysis, ground motion selection, and nonlinear dynamic analysis are performed, using the conditional spectra with varying conditioning periods, to assess the performance of a 20‐story reinforced concrete frame structure. It is shown here that risk‐based assessments are relatively insensitive to the choice of conditioning period when the ground motions are carefully selected to ensure hazard consistency. This observed insensitivity to the conditioning period comes from the fact that, when CS‐based ground motion selection is used, the distributions of response spectra of the selected ground motions are consistent with the site ground motion hazard curves at all relevant periods; this consistency with the site hazard curves is independent of the conditioning period. The importance of an exact CS (which incorporates multiple causal earthquakes and ground motion prediction models) to achieve the appropriate spectral variability at periods away from the conditioning period is also highlighted. The findings of this paper are expected theoretically but have not been empirically demonstrated previously. Copyright © 2013 John Wiley & Sons, Ltd.     

Climate change impacts on U.S. Coastal and Marine Ecosystems

Increases in concentrations of greenhouse gases projected for the 21st century are expected to lead to increased mean global air and ocean temperatures. The National Assessment of Potential Consequences of Climate Variability and Change (NAST 2001) was based on a series of regional and sector assessments. This paper is a summary of the coastal and marine resources sector review of potential impacts on shorelines, estuaries, coastal wetlands, coral reefs, and ocean margin ecosystems. The assessment considered the impacts of several key drivers of climate change: sea level change; alterations in precipitation patterns and subsequent delivery of freshwater, nutrients, and sediment; increased ocean temperature; alterations in circulation patterns; changes in frequency and intensity of coastal storms; and increased levels of atmospheric CO₂. Increasing rates of sea-level rise and intensity and frequency of coastal storms and hurricanes over the next decades will increase threats to shorelines, wetlands, and coastal development. Estuarine productivity will change in response to alteration in the timing and amount of freshwater, nutrients, and sediment delivery. Higher water temperatures and changes in freshwater delivery will alter estuarine stratification, residence time, and eutrophication. Increased ocean temperatures are expected to increase coral bleaching and higher CO₂ levels may reduce coral calcification, making it more difficult for corals to recover from other disturbances, and inhibiting poleward shifts. Ocean warming is expected to cause poleward shifts in the ranges of many other organisms, including commercial species, and these shifts may have secondary effects on their predators and prey. Although these potential impacts of climate change and variability will vary from system to system, it is important to recognize that they will be superimposed upon, and in many cases intensify, other ecosystem stresses (pollution, harvesting, habitat destruction, invasive species, land and resource use, extreme natural events), which may lead to more significant consequences.     

The Aitik Cu–Au–Ag deposit in northern Sweden: a product of high salinity fluids

The Aitik Cu–Au–Ag deposit is located in northern Sweden and is hosted by strongly deformed 1.9 Ga Svecofennian volcano-sedimentary rocks. The main copper mineralization, which occurs as disseminations and veinlets, is hosted by garnet–biotite schist. Subeconomic mineralization in the footwall to the ore is hosted by feldspar–biotite–amphibole gneiss and porphyritic quartz monzodiorite. The deposit has been affected by post-mineralization metamorphic and igneous activity. Fluid inclusions in six samples of copper-mineralized quartz veins record the presence of three different fluid populations. The main ore was deposited from an aqueous, highly saline (31–37 eq. wt% NaCl + CaCl₂) fluid. This fluid was trapped in inclusions intimately associated with the main chalcopyrite mineralization. Later bornite deposition took place from a less saline (18–27 eq. wt% NaCl + CaCl₂), aqueous fluid. A third fluid composed of almost pure CO₂, interacted with the copper-rich system during a post-ore event. The Aitik Cu–Au–Ag deposit shares some features with both porphyry-type and Fe-oxide–Cu–Au deposits. A high calcium content of the ore fluids, similar to other Cu–Au deposits in northern Scandinavia, suggests a contribution to the salinity of the mainly magmatic-hydrothermal fluids from evaporitic rocks in stratigraphically lower units.     

Jahreszeitliche ökologische Beobachtungen an Foraminiferen im Limski kanal bei Rovinj/Jugoslawien (nördliche Adria)

Zusammenfassung Als Vorbericht einer Dissertation über ökologische Beobachtungen an Foraminiferen im Limski kanal wurde diese Arbeit auf der 60. Jahrestagung der Geologischen Vereinigung im Februar 1970 in Kiel referiert. Räumliche und zeitliche Verteilung benthonischer Foraminiferen im Limski kanal werden diskutiert. Jahreszeitliche Schwankungen in der prozentualen Zusammensetzung der drei großen Gruppen hyaliner, porzellanschaliger und agglutinierender Formen und auch einzelner Arten in der Lebend-Fauna können gezeigt werden. Ein Vergleich von Biocoenose und Thanatocoenose ergibt Unterschiede in der Zusammensetzung, wahrscheinlich eine Folge von Bioturbation. Untersuchungen von Lebend-Fauna in Sediment-Kernen, durchgeführt in cm-Intervallen, scheinen die Annahme zu bestätigen, daß Foraminiferen in offenen Bauten von Endobenthos leben können. Dort erreichen sie Konzentrationen, die etwa 8–10mal höher sein können als in normalen Oberflächen-Proben, bezogen auf eine definierte Fläche.

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This preliminary note of a thesis dealing with ecological observations of foraminifera in the Limski kanal was reported during the 60th annual meeting of the Geologische Vereinigung in Kiel, February 1970. Spatial and seasonal distributions of benthonic foraminifera in the Limski kanal are discussed. Percentage relations of the three major groups, hyaline, porcelaneous and agglutinated forms and also of single species, show seasonal variations in the living fauna. A comparison between the biocenosis and the thanatocenosis reveals differences in the faunal composition, probably caused by bioturbation. Research into the living fauna carried out in two sediment-cores, which were cut in cm-intervals, seem to prove the assumption that foraminifera are able to live in open burrows of endobenthos. There they can attain concentrations which are about 8 to 10 times higher than in normal surface samples, referred to a defined area.

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Résumé Cette note préliminaire d'une thèse traitant des observations écologiques sur les foraminifères benthoniques dans le Limski kanal a été présentée à l'assemblée annuelle de la Geologische Vereinigung à Kiel au mois de février 1970. La distribution spatiale et saisonnière des foraminifères a été étudiée; les relations (en pour cent) des trois groupes majeurs de foraminifères: hyalin, porcellainier et agglutinant et aussi des espèces singulières dénotent des variations saisonnières. Une comparaison entre la biocénose et la thanatocénose révèle des différences en ce qui concerne la composition, différences probablement causées par la bioturbation intensive au fond du Limski kanal. En recherchant les foraminifères vivants (colorés) dans deux carottes coupées à intervalles réguliers d'un cm, l'hypothèse que les foraminifères vivent en terriers ouverts de l'endobenthos semble être vérifiée. Ils peuvent atteindre ici des concentrations 8 à 10 fois plus hautes que celles des échantillons «normaux» tirées de la surface du sédiment en se réfèrent à une aire bien définie.

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Tracking provenance of earth science data

Tremendous volumes of data have been captured, archived and analyzed. Sensors, algorithms and processing systems for transforming and analyzing the data are evolving over time. Web Portals and Services can create transient data sets on-demand. Data are transferred from organization to organization with additional transformations at every stage. Provenance in this context refers to the source of data and a record of the process that led to its current state. It encompasses the documentation of a variety of artifacts related to particular data. Provenance is important for understanding and using scientific datasets, and critical for independent confirmation of scientific results. Managing provenance throughout scientific data processing has gained interest lately and there are a variety of approaches. Large scale scientific datasets consisting of thousands to millions of individual data files and processes offer particular challenges. This paper uses the analogy of art history provenance to explore some of the concerns of applying provenance tracking to earth science data. It also illustrates some of the provenance issues with examples drawn from the Ozone Monitoring Instrument (OMI) Data Processing System (OMIDAPS) (Tilmes et al. 2004) run at NASA’s Goddard Space Flight Center by the first author.     

A 10,000-year high-resolution diatom record from Pilkington Bay, Lake Victoria, East Africa

A new diatom record from Lake Victoria’s Pilkington Bay, subsampled at 21- to 25-year intervals and supported by 20 AMS dates, reveals a ∼10,000 calendar year environmental history that is supported by published diatom and pollen data from two nearby sites. With their chronologies adjusted here to account for newly documented ancient carbon effects in the lake, these three records provide a coherent, finely resolved reconstruction of Holocene climate change in equatorial East Africa. After an insolation-induced rainfall maximum ca. 8800-8300 cal yr B.P., precipitation became more seasonal and decreased abruptly ca. 8200 and 5700 yr B.P. in apparent association with northern deglaciation events. Century-scale rainfall increases occurred ca. 8500, 7000, 5800, and 4000 yr B.P. Conditions after 2700 yr B.P. were generally similar to those of today, but major droughts occurred ca. 1200-600 yr B.P. during Europe’s Medieval Warm Period.     

The relative contribution of processes driving variability in flow, shear, and turbidity over a fringing coral reef: West Maui, Hawaii

High-frequency measurements of waves, currents and water column properties were made on a fringing coral reef off northwest Maui, Hawaii, for 15 months between 2001 and 2003 to aid in understanding the processes governing flow and turbidity over a range of time scales and their contributions to annual budgets. The summer months were characterized by consistent trade winds and small waves, and under these conditions high-frequency internal bores were commonly observed, there was little net flow or turbidity over the fore reef, and over the reef flat net flow was downwind and turbidity was high. When the trade winds waned or the wind direction deviated from the dominant trade wind orientation, strong alongshore flows occurred into the typically dominant wind direction and lower turbidity was observed across the reef. During the winter, when large storm waves impacted the study area, strong offshore flows and high turbidity occurred on the reef flat and over the fore reef. Over the course of a year, trade wind conditions resulted in the greatest net transport of turbid water due to relatively strong currents, moderate overall turbidity, and their frequent occurrence. Throughout the period of study, near-surface current directions over the fore reef varied on average by more than 41° from those near the seafloor, and the orientation of the currents over the reef flat differed on average by more than 65° from those observed over the fore reef. This shear occurred over relatively short vertical (order of meters) and horizontal (order of hundreds of meters) scales, causing material distributed throughout the water column, including the particles in suspension causing the turbidity (e.g. sediment or larvae) and/or dissolved nutrients and contaminants, to be transported in different directions under constant oceanographic and meteorologic forcing.     

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